Current Federal drug rules list marijuana as a Schedule I drug, along with LSD and heroin. Meanwhile, 14 states have laws that permit people with medical conditions like cancer and chronic pain to possess and use marijuana without fear of prosecution.

This confusing situation turns chaotic when it comes to the field of employment law. For example, the Supreme Courts in Oregon, California and Montana—states with permissive laws about possession and use of cannabis—have allowed employers to fire medical-marijuana patients for using the drug. In other states like Maine and Rhode Island, medical-marijuana laws proscribe such behavior.

A pending lawsuit in Michigan might clarify matters. In that case, Joseph Casias, a Michigan resident who uses the drug to control pain associated with a brain tumor, has sued Wal-Mart, his employer, after the retailer fired him for failing a drug test on the job.

Casias claims he uses marijuana legally according to Michigan law. He takes the drug at night and has never come to work high. The drug test was administered per company policy after he strained his knee one day at work.

A Wal-Mart spokesman told the Wall Street Journal that Casias’ case was “unfortunate,” adding that “as more states allow this treatment, employers are left without any guidelines except the federal standard. Until further guidance is available, we will default to what we believe is the safest environment for our associates and customers.”

No one suggests that workers should be permitted to use marijuana on the job. But advocacy groups suggest that if employees show no clear signs of impairment, employers should assume those with valid medical-marijuana registration cards are taking the drug responsibly.

That doesn’t sit well with some employers, who cite statistics showing that cannabis is implicated more frequently than any other drug in workplace accidents causing injury or property damage. Time to fix this, fellas.